Commercially available printer technology for use by everyday consumers has evolved to a point where very high-resolution images can be transferred to various types of media, including paper. Ink-jet printing is a very popular and effective process for achieving high quality images, high speed, and affordable results. Ink-jet printing involves the placement of small drops of a fluid ink onto a media surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. Within this general technique, the specific method used to deposit the ink-jet ink onto the printing surface varies from system to system, and can include continuous ink deposit and drop-on-demand ink deposit. Regarding drop-on-demand printing systems, the ink-jet inks are typically based upon water and solvents such as glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave such that substantially all of the ink droplets ejected are used to form the printed image.
In general, ink-jet inks are either dye- or pigment-based inks. Both are typically prepared in an ink vehicle that contains the dye and/or the pigment. Dye-based ink-jet inks generally use a soluble colorant that is usually water-based. Conversely, pigmented inks typically use an insoluble or dispersed colorant to achieve color.
There are several reasons that ink-jet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, capability of high-speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers.
Such improvements, while tremendously positive, have sparked increased demands by consumers in this area, e.g., higher speeds, higher resolution, full color image formation, increased stability, etc. As new ink-jet inks are developed, there have been several traditional characteristics to consider when evaluating the ink in conjunction with a printing surface or substrate. Such characteristics include edge acuity and optical density of the image on the surface, uniformity of optical density and color in printed regions, black to color bleed control, dry time of the ink on the substrate, adhesion to the substrate, lack of deviation in ink droplet placement, presence of all dots, resistance of the ink after drying to water and other solvents, long term storage stability, long term reliability without corrosion or nozzle clogging, and short term latency during printing.
Though the above list of characteristics provides a worthy goal to achieve, there are difficulties associated with satisfying all of the above characteristics. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, most commercial inks for use in ink-jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
Furthermore, dye-based ink-jet inks tend to have edge acuity and accuracy of droplet placement that are generally inferior to pigment-based ink-jet inks. Thus, there has been increased interest in improving print quality resulting from the use of dye-based ink-jet inks. One characteristic of many ink-jet inks is the tendency of the ink to dry and/or partially agglomerate to form obstructions at the exit of the nozzles. More specifically, during ink-jet printing, a plurality of nozzles, e.g., 48 to 320 are used with each nozzle experiencing periods of non-use while also being exposed to the air. This period of non-use during printing can often allow the more volatile components of the ink to evaporate and thus produce solids which can block the nozzle or cause redirection of the ink droplets.
Most ink-jet printing systems include a mechanism which allows for servicing of the nozzles to remove material which tends to block the nozzles. However, these service operations entail increased time to perform and can reduce the useful life of the print mechanisms. For example, to avoid the problems associated with decap, pens can be fired periodically at times other than when printing on a desired substrate, resulting in wasted ink-jet ink. Thus, increasing slewing decap time can reduce waste of ink-jet ink and reduce wear on the printer. One method of increasing slewing decap time can involve increasing the kinetic energy of the drop ejected from the pen. However, increasing kinetic energy can also increase the spray, drop weight, and/or other image quality degrading characteristics. Other approaches have also been attempted with varying degrees of success.
Accordingly, investigations continue into developing ink formulations that have improved properties and that do not improve one property at the significant expense of the others. Many challenges still remain to further improve the image quality and stability of ink-jet inks without sacrificing pen performance and reliability.